The present invention relates to an optical storage device, and more particularly, to a method for determining a relationship between difference of object lens location and a driving control effort in an optical storage device and apparatus thereof.
A personal computer (PC) or other electronic system often includes an optical storage device, which has become a widely applied storage medium. FIG. 1 shows a block diagram of a conventional optical storage device 100. In FIG. 1, the optical storage device 100 comprises a spindle motor 110, an optical disc 120, a pickup head 130, a signal processing unit 140, a focusing controller 150, a micro controller unit (MCU) 160, and a power driver 170. The optical disc 120 is of CD or DVD type, which contains at least two layers: a surface layer and a reflective layer. The surface layer is defined as the disc surface at the side towards to the pickup head. The reflective layer is defined as the junction layer between the protective material and metal surface on which the information pits is located. Normally, there is one DVD laser diode (LD) and one CD laser diode installed on the pickup head 130. An object lens is used to focus the laser light generate by the DVD laser diode or the CD laser diode onto the optical disc 120, then the pickup head 130 can reproduce the data stored on the optical disc 120 according to received reflected light. A focusing actuator, also called a focusing coil, of the pickup head moves the object lens perpendicular to the surface of the optical disc 120 according to a driving control effort (in this example, the driving control effort is a driving voltage) generated by the power driver 170, hence the location of a focal point of the laser light generated by one of the LDs can be controlled.
When controlling the focal point of the laser light to jump between different layers of the optical disc 120, or processing an optical disc identification procedure, the driving voltage used to drive the focusing actuator would continuously be altered. By altering the driving voltage, the object lens can be moved, hence the location of focal point of the laser light can be controlled. The relationship between the moving distance of the object lens and the difference of two values of the driving voltage can be expressed as a displacement gain, wherein the units of the displacement gain is distance/voltage. The displacement gain can also be thought of as a DC sensitivity of the focusing actuator.
Take the optical disc identification procedure as an example. By measuring the time for the focal point of the laser light generated by one of the LDs to move between a surface layer and a reflective layer of the optical disc 120, or by measuring the voltage change of the driving voltage, the distance between the surface layer and the reflective layer can be determined according to the measuring result and a predetermined displacement gain of the focusing actuator. Roughly speaking, an optical disc with shorter distance between the surface layer and the reflective layer will be identified as a DVD type optical disc. An optical disc with longer distance between the surface layer and the reflective layer will be identified as a CD type optical disc.
Optical storage devices of the prior art use a fixed value as the predetermined displacement gain of the focusing actuator, and use the fixed displacement gain as a parameter to process procedures such as the layer jump procedure or the optical disc identification procedure. However, because there are always slight differences between each focusing actuator, it is almost impossible to manufacture optical storage devices having a common and exact value on the displacement gain. Hence, it's apparent that using a common and fixed value as the displacement gain for each optical storage device is not the best solution.